1. Field of the Invention
The present invention relates to a high strength coupling which transfers axial force and torque from one member to another via a key and keyway arrangement.
2. Description of the Prior Art
Many types of couplings have been used to connect one cylindrical member to another. In many instances, it is necessary to transfer axial force and torque from one shaft or pipe member to a second shaft or pipe member. Oftentimes, it is desirable that the coupling be easy to connect and disconnect which eliminates connecting the members by a permanent means such as welding.
Threaded couplings have been used to provide a quick connect/disconnect coupling. Threaded couplings transfer axial compressive and tensile forces and torque in one direction about the longitudinal axis. Threaded couplings have the disadvantage in that the threaded coupling will not take high torque loads in both the clockwise and counter-clockwise directions due to the threaded make-up of the coupling. Furthermore, the threaded coupling is extremely difficult to disconnect after prolonged periods of torque transfer due to the frictional engagement of the threads. Threaded couplings are also subject to damaged threads and cross-threading during the coupling make-up which can result in the replacement of the coupling member.
Various arrangements of keys and keyways have been used to form axial load and torque transferring couplings as, for example, shown in U.S. Pat. Nos. 4,893,962, 3,433,512, 3,315,993, 2,756,022, and 2,032,491. Typically, in key/keyway couplings, the key is subjected to shear stress both by the torque and the axial load. Shear stress is directly proportional to the cross-sectional area of the key in shear. The maximum design rating for the coupling is often limited by the shear stress of the key.
U.S. Pat. No. 573,695 discloses a coupling for joining an inner cylindrical tube to an outer cylindrical tube wherein the inner cylindrical tube includes a transverse keyway and the outer cylindrical tube includes a transverse slot. A key having an arcuate surface extends through the slot and into the keyway. A retaining band is driven over the arcuate surface of the key thereby forcing the key inward to complete the joint. The downward pressure applied to the key by the retaining band causes the inner tube to expand somewhat or spring into more intimate binding contact with the outer tube.
U.S. Pat. No. 2,756,022 discloses a shock absorber coupling wherein an inner cylindrical tube is joined to an outer cylindrical tube. The inner cylindrical tube includes a longitudinal keyway and the outer cylindrical tube includes an elongated longitudinal slot. A rectangular key extends through the longitudinal slot and into the longitudinal keyway. A retaining sleeve is positioned over the longitudinal keyway and the rectangular key to maintain the connection of the inner and outer cylindrical members.
It is desirable to have a high strength coupling which can transfer both axial tensile and compressive forces and torque in both directions around the longitudinal axis of the connected members. The high strength coupling should be of simple construction, low cost and quick and easy to connect and disconnect.